Metal plate rocker arm and method of manufacturing the metal plate rocker arm

ABSTRACT

A sheet-metal rocker arm formed by the steps of punch-pressing a sheet of metal member to form a blank having a predetermined shape and a through-hole, of subjecting the blank to a bending process based on pressing to form a pair of substantially parallel side wall sections and a connection section for connecting the widthwise edges of the both side wall sections and to form at least one pair of circular holes in the both side wall sections at locations in alignment, of deforming the middle of the connection section in the thickness direction to form an engagement portion on one side of the connection section such that the engagement portion is recessed from the other portion of the connection section, and of forming on the other side of the connection section a bulge section, trapezoidal in cross section, which protrudes in an embanked-shape as the engagement portion is formed, whereby the widthwise edges of the middle of the bulge section corresponding to the top edge of the trapezoidal shape exist on the widthwise inside of the both widthwise edges of the engagement portion.

FIELD OF THE INVENTION

This invention relates to a rocker arm that is installed in the valvemechanism of an engine for transforming the rotation of the camshaft toreciprocating motion of the valve unit (intake valve and exhaust valve),and more particularly to improvement of a rocker arm made of sheet-metalby pressing process.

BACKGROUND OF THE INVENTION

In reciprocating engines (reciprocating piston engines), except for some2-cycle engines, there is an intake valve and an exhaust valve that openand close in synchronization with the rotation of the crankshaft. Inthis kind of reciprocating engine the movement of the cam shaft, whichrotates in synchronization with the rotation of the aforementionedcrankshaft (at ½ the rpm in the case of a 4-cycle engine), istransmitted to the aforementioned intake valve and exhaust valve throughthe rocker arm, to cause the intake valve and exhaust valve to moveback-and-forth in the axial direction.

Conventionally, it has been typical for the rocker arm installed in thevalve mechanism of this kind of engine to be a molding (cast iron oraluminum die cast article). However, moldings are heavy (in the case ofcast iron) or have a large volume in order to maintain sufficientstrength (in the case of cast aluminum parts). Moreover, since in mostcases the moldings are made using a lost wax process, it is difficult toavoid high manufacturing cost. Therefore, recently, manufacture theaforementioned rocker arm by pressing a sheet metal such as steel sheethas been considered and has been performed in some cases.

The manufacturing method of a this kind of rocker arm made of sheetmetal has been disclosed previously, for example as disclosed inJapanese Patent Publication No. Tokukai Hei 3-172506. In themanufacturing method described in this publication, the sheet metalrocker arm is manufactured in one piece by pressing a single sheet ofsheet metal. Therefore, the sheet metal rocker arm that is obtained hasa nearly uniform thickness over its entire surface.

In contrast to this, a rocker arm that is manufactured by joining orwelding two or three members together that are each formed by pressingsheet metal has been known. With this construction, the thickness ofeach of these members is the same, however, in the case of a rocker armthat is formed by combining a plurality of members in this way, thethickness of the connection section, including the pivot section and thevalve engagement, can be made larger than the wall sections.

Of the prior art described above, in the case of Japanese PatentPublication No. Tokukai Hei 3-172506 where the sheet-metal rocker arm ismade from one sheet of metal, the thickness of the sheet metal rockerarm is nearly uniform over the entire surface, so the area around thevalve engagement that receives strong forces during use, has a largestrength disadvantage compared with other parts and rigidity may alsobecome low. When the thickness of the metal sheet used for making thesheet metal rocker arm is increased in order to sufficiently secure thestrength and rigidity of the area near the valve engagement, thethickness of the other parts becomes greater than necessary, making itimpossible to sufficiently make the sheet-metal rocker arm compact andlightweight, and also increases the cost of material.

On the other hand, in the case of a sheet-metal rocker arm that is madeby welding together two or three members that are formed by pressingsheet metal, the thickness of the connection section, including thevalve engagement, can be made thicker than other parts, such as the wallsections, however, after the members have been individually made, theymust be combined and joined together by welding. Therefore, the numberof processing steps increases, and managing the parts can betroublesome. Furthermore, complicated, precision equipment is necessaryfor positioning the parts when putting them together, so in addition tothe increase in the number of processing steps and the need for managingthe parts, it is impossible to avoid increased manufacturing cost.Moreover, the quality (precision) of the sheet-metal rocker arm isinferior when compared with a rocker arm made in one piece.

In order to solve the problems mentioned above, an invention wasdisclosed in Japanese Patent Publication No. Tokukai Hei 11-63515, asshown in FIGS. 1 thru 7, relating to sheet-metal rocker arm and themanufacturing method thereof. As shown in FIG. 1, the sheet-metal rockerarm of this previous invention comprises a pair of wall sections 2 thatare nearly parallel with each other, and a first connection section 3and second connection section 4 that connect one of the edges in thewidth direction of both of the wall sections 2 together, respectively.Moreover, a pair of concentric circular holes 5 is formed in the middlein the lengthwise direction of both of these wall sections 2, and bothends of a support shaft for supporting the roller that interacts withthe cam are supported in these holes 5 such that the roller rotatesfreely. Of the first connection section 3 and the second connectionsection 4, an engagement section 6 is formed on one surface of the firstconnection section 3 for coming into contact with the base of the valveunit, and a second engagement section 7 is formed on the secondconnection section 4 for coming into contact with the tip end of a rushadjuster.

Of the first engagement section 6 and the second engagement section 7,the first engagement section 6 is formed on its one surface into aconcave channel shape by plastic deformation in the thickness directionin the middle in the width direction of the first connection section 3such that it is depressed more than the other parts of the firstconnection section 3. Also, there is a raised section 8 on the othersurface of the first connection section 3, having a trapezoidalcross-section that is protruded outward in a banked shape as the firstengagement section 6 is formed. On the other hand, the second connectionsection 7 is formed into a spherical concave shape by plasticdeformation in the thickness direction in the center of the secondconnection section 4.

When making the sheet-metal rocker arm as described above, first, in afirst process, a first blank 9 is made as shown in FIG. 2. In otherwords, in this first process, a metal sheet (flat sheet or coiled sheet)such as a carbon steel sheet with a thickness of 3 to 4 mm and havingsufficient rigidity is supplied between the punching die and cradle dieof a press apparatus (not shown in the figure), and the first blank 9 ispunch-pressed and formed between these two dies.

As shown in FIG. 2(A), this first blank 9 has a nearly diamond shapewith rounded corners and with one end in the lengthwise direction (rightend in FIG. 2(A)) cut off, and has a thickness t₉ (FIG. 2(B)). In thecenter in the width direction (up and down directions in FIG. 2(A)) ofthis first blank 9, in the section slightly inside of the two dot-dashedlines α shown in FIG. 2(A) (the center in the width direction), theportion with width W₁₀ is a base section 10 that is continuous inlengthwise direction (left and right directions in FIG. 2(A)) of thefirst blank 9. On both sides in the width direction of this base section10 there is a pair of nearly triangular wing-shaped sections 11.

Next, in a second process, a through hole 12 is formed in the center ofthe first blank 9 as shown in FIG. 3(A), to become the second blank 13.The shape of this through hole 12 is formed in nearly an hourglass shapewith the center section in the lengthwise direction of both edges in thewidth direction formed with a pair of tongue-shaped sections 14 in apartial arc shape protruding toward each other. These two tongue-shapedsections 14 are provided for forming circular holes 5 (see FIG. 1 andFIG. 7) for supporting both ends of a support shaft for supporting aroller, to be described later, such that it rotates freely. In addition,semi-circular cutout sections 15 are formed in each of the four cornersof the through hole 12. These cutout sections 15 are provided for makingit easier in the third process to bend the base section 10 in an arcshape in cross section to form a curved section 16 (see FIG. 4).

This second blank 13 described above is formed by supplying the firstblank 9 between the punching die and cradle die of a press apparatus(not shown) and punching out the through hole 12 between these two dies.The width W₁₀ of the base section 10 of the first blank 9 and secondblank 13 is wider than the width W₁₇ (W₁₀>W₁₇) of a first intermediateblank 17 (see FIG. 4) which is the distance between the outer sides of apair of wall sections 2 that are formed ill the third process describednext. As the width W₁₀ of the base section 10 is made wider than thewidth W₁₇ of first intermediate blank 17, the distance D₁₄ between thepair of tongue-shaped sections 14 is also made large.

When the distance D₁₄ between the pair of tongue-shaped sections 14 ismade large in this way, it is possible to secure the life of thepunching die used for punching out the aforementioned through hole 12.In other words, when the width of the center section of the through hole12 is narrow, the load on the punching die used for punching out thisthrough hole is large, which shortens the life of the punching die. Onthe other hand, when the width of the center section of the through hole12, that is the distance D₁₄ between the pair of tongue-shaped sections14, is large, the load on the punching die used for forming the throughhole 12 is decreased, making it possible to secure the durability of thepunching die, and thus making it possible to reduce costs.

As to the order of forming the second blank 13, it is also possible tofirst, form the through hole 12 instead of by the second processdescribed above, then to form the base section 10 and wing-shapedsection 11 instead of by the first process. Furthermore, if the capacityof the press apparatus is sufficient and the punching die and cradle dieare capable, it is possible to directly form the second blank 13, asshown in FIG. 3, from the sheet metal material.

In either case, the second blank 13 that is formed in the shape shown inFIG. 3 is then formed into the first intermediate blank 17, as shown inFIG. 4, by the following third process. In the third process, the secondblank 13 is supplied between the pressing die and cradle die of a pressapparatus (not shown in the figure), and strongly pressed to bend thebase section 10 and wing-shaped sections 11 of the second blank 13. Thissecond blank 13 is formed into a first intermediate blank 17, having apair of wall sections 2 on the left and right in the width direction,and a curved section 16 for connecting the edges in the width direction(left and right directions in FIGS. 4(C) and 4(D)) of these wallsections 2. This curved section 16 is formed in a semi-cylindrical shapesuch that it is discontinuous in a portion that corresponds to thethrough hole 12 in the center in the lengthwise direction (left andright directions in FIG. 4(A)) of the first intermediate blank 17. Ofthe curved section 16 that is divided into two by the through hole 12 inthis way, the portion on one end side (right end side in FIG. 4(A))becomes the engagement section 6 that comes in contact with the base ofthe valve knit, and the portion on other end side (left end side inFIGS. 4(A) and 4(B)) becomes the second engagement section 7 (see FIG.1, FIG. 6 and FIG. 7) that comes in contact with the tip end of a rushadjuster.

As described above, the width W₁₇ of the first intermediate blank 17,which is the distance between the outside surfaces of the pair of wallsections 2, is smaller than the width W₁₀ of the base section 10 of thefirst and second blanks 9 and 13. In other words, the curved section 16in the first intermediate blank 17, which acts as the connection sectionfor connecting the edges in the width direction of the pair of wallsections 2, is formed in a semi-cylindrical shape as shown in FIGS. 4(C)and 4(D). Since the width of this semi-cylindrical curved section 16 isless than the width W₁₀ of the flat base section 10 which is to beformed into the semi-cylindrical carved section 16, it is possible tomake the width W₁₀ of this base section 10 larger than the width W₁₇ ofthe first intermediate blank 17, that is the distance between the pairof left and right wall sections 2, 2 (W₁₀>W₁₇), and thus it is possibleto make the distance D₁₄ between the pair of tongue-shaped sections 14large. The thickness t₁₆ of the curved section 16 of the firstintermediate blank 17 shown in FIG. 4, which is obtained from the thirdprocess described above, is nearly the same as the thickness t₉ of thefirst blank 9 (t₁₆≈₉).

Next, in a fourth process, pressing is performed for at least one end ofthe curved section 16 that forms the engagement section 6 that comes incontact with the base end of the valve unit, in order to increase thethickness. In this case, in order to obtain the desired thickness afterthe pressing process, it is necessary to regulate the shape anddimensions of the curved section 16. In other words, selecting the sizeand dimensions of the curved section 16 determines the aforementionedthickness in the pressing process. Moreover, at the same time that thecurved section 16 is formed on the first intermediate blank 17, the pairof left and right wall side sections 2 is also formed. In other words,as the curved section 16 is formed, the wing-shaped sections 11, whichare formed on both ends in the width direction of the first and secondblanks 9 and 13, and the tongue-shaped sections 14, which are formed onthe inner edges in the through-hole 12 in the center of the second blank13, are raised upright such that they become the pair of nearly parallelside wall sections 2.

In the fourth process, the curved section 16 of the first intermediateblank 17, which is formed as described above, is pressed to form thesecond intermediate blank 18 as shown in FIG. 5. In other words, in thefourth process, the curved section 16 is flattened and its thickness isincreased to form a connection section 3 and second connection 4 havingthick nesses t₃ and t₄, which are greater than the thickness t₉ (seeFIG. 2B) of the first blank (t₉<t₃, t₄). The curved section 16 does notneed to be a semi-circular cylindrical shape, but can be curved in asemi-oval or semi-elliptical cylindrical shape etc.

The fourth process mentioned above is performed by setting the curvedsection 16 of the first intermediate blank 17 between a pressing die forpressing and a cradle die and performing cold forging by pressing toplastically deform the curved section 16. As a result, a flat connectionsection 3 and second connection 4 are formed. When plastically deformingthe curved section 16 to form the connection section 3 and secondconnection section 4, as the curved section 16 with arc-shapedcross-section is deformed to become the flat connection section 3 andsecond connection section 4, they are thickened to the thickness t₃ andt₄. In this way, the process where the thickness is increased at thesame time as the curved section 16 with arc-shaped cross-section isdeformed to become the flat connection section 3 and second connectionsection 4, can be easily performed by pressing with a press.

In the example shown in the figures, the thickness of connection section3 formed on one side is increased as well as the thickness of the secondconnection section 4 that is formed on the other side is increased.However, when the sheet-metal rocker arm is in operation, an especiallylarge stress is applied to the connection section 3 provided with theengagement section 6 that comes in contact with the base end of thevalve unit. Therefore, the thickness of the second connection section 4on the other side must not necessarily increased. When it is notnecessary to increase the thickness, the curved section 16 can beplastically deformed to simply form a flat connection section. However,by making the thickness of the connection section 3 and secondconnection section 4 the same less processing is required, which isadvantageous from the aspect of cost.

In the fourth process, when the connection section 3 and secondconnection section 4 with a relatively large thickness are formed in thefirst intermediate blank 17 to make a second intermediate blank 18, thenin the fifth process a plastic deformation process or cutting process,and when necessary a grinding process, is performed for the connectionsection 3 and second connection section 4. In other words, as shown inFIG. 6, the engagement section 6, which comes in contact with the baseend of the valve unit (not shown in the figure), is formed on theconnection section 3. Moreover, the second engagement section 7, whichcomes in contact with the tip end of a rush adjuster, is formed on thesecond connection section 4. In this fifth process, the connectionsection 3 of the second intermediate blank 18 is set between thepressing die and cradle die of a forging apparatus to perform coldforging of the connection section 3 to form a concave engagement section6 with a bottom surface that is curved in a convex shape as shown inFIGS. 6(A), 6(B) and 6(D). Moreover, the second connection section 4 isset between the pressing die and cradle die of a different forgingapparatus (not shown in the figure) to perform cold forging of thissecond connection section 4 to form a spherical concave hole or secondengagement section 7, as shown in FIG. 6(A), 6(B) and 6(C). From thisfifth process, an engagement section 6 and second engagement section 7are formed on the respective connection section 3 and second connectionsection 4, which have thicknesses that are greater than the thickness ofthe first blank 9, to form the third intermediate blank 19. The order ofthe processes from the first to fifth can be changed. For example, it ispossible to change the order of the processes above or the shape of theintermediate blanks such that they are suitable for transfer-pressprocessing or progressive processing. However, in the end, the thirdintermediate blank 19 should be obtained.

The third intermediate blank 19 that is obtained in this way isprocessed in the sixth process by pressing or drilling to form circularholes 5 at matching positions in the middle of the pair of side wallsections 2 to form the completed sheet-metal rocker arm 1 as shown inFIG. 1 and FIG. 7. As described above, both of these circular holes 5are provided for supporting both of the ends of a support shaft thatrotatably supports the roller. In other words, the roller is supportedin the middle of the support shaft whose ends are supported in theaforementioned circular holes 5 such that the roller rotates freely, andthe outer peripheral surface of the roller comes in contact with theouter peripheral surface of the cam to transform the rotating motion ofthe cam shaft to rocking motion of the sheet-metal rocker arm 1.

The sheet-metal rocker arm and the manufacturing method for it of theprevious invention described above, not only makes it possible toimprove the strength and rigidity of the rocker arm, but by reducing thenumber of processes and parts, also make it possible to reduce cost,improve precision and simplify the equipment used.

However, in order for it to obtain more strength so as to be possible toinstall the rocker arm in an engine with large output, improvements ofthe following aspect related to the engagement section 6 that comes incontact with the base of the valve unit are desired. In this case, it isdifficult, with the manufacturing method for the sheet-metal rocker armof the previous invention described above, to improve this aspect.

This aspect will be explained using FIG. 8, which shows thecross-section shape of the engagement section 6 that is formed on thesheet-metal rocker arm 1 of the previous invention described above. Bydeforming the middle of the connection section 3 in the thicknessdirection, the aforementioned engagement section 6 is formed such thatone surface (bottom surface in FIG. 8) of the connection section 3 ismore concave than other sections of the connection section 3, and thereis a bulge section 8 with a trapezoidal-shaped cross-section thatprotrudes in the shape of an embankment on the other surface (topsurface in FIG. 8) of the connection section 3. In the case of theconventional construction, the width W₂₀ of the center of this bulgesection 8, which corresponds to the top of the trapezoidal shape incross section of this bulge section 8, was the same as or greater thanthe width W₆ of the aforementioned engagement section 6 (W₂₀≧W₆). Inaddition, both edges in the width direction (left and right direction inFIG. 8) of the center section 20 are in nearly the same position as oroutside of in the width direction of both edges in the width directionof the engagement section 6.

The aforementioned engagement section 6 and bulge section 8 are formedby pressing tightly a portion, corresponding to the connection section 3on the end of the second intermediate blank 18, in the fifth process,between the pressing die and cradle die of a press apparatus. At thattime, when the width W₂₀ of the center section 20 of the bulge section 8is the same as or greater than the width W₆ of the engagement section 6,a shear force is applied to part in the width direction of theconnection section 3 at both ends in the width direction of theengagement section 6 (section shown by the dot-dash line β in FIG. 8).As a result, internal distortion occurs in this section, and not onlydoes it become easy for cracking or the like to occur duringmanufacture, but there is also a possibility that damage such ascracking could occur at both ends in the width direction of theengagement section 6.

The force applied to the engagement section 6 during operation becomeslarge as the spring force of the return spring to energize the valveunit whose base section comes in contact with the engagement section 6is made large in order that the output of the engine becomes large.Also, in order to be able to install the sheet-metal rocker arm in ahigh-output engine and to secure sufficient durability, it is desiredthat the strength of the engagement sections 6 be increased.

In order to accomplish that, it is also desired that the thickness ofthe engagement section 6 be increased, however in the manufacturingmethod of the previous invention described above, the amount that thethickness can be increased is limited to about 5 to 40% of the thicknessof the raw sheet. For example, it is difficult to increase the thicknesst₃ of the connection section 3 of the engagement section 6 to nearly twotimes or more than two times the thickness t, of the pair of side wallsections 2.

In consideration of the problems described above, an objective of thisinvention is to provide a sheet-metal rocker arm and manufacturingmethod that solves these problems.

BRIEF DESCRIPTIONS OF THE INVENTION

FIG. 1 is a perspective view of a sheet-metal rocker arm according tothe previous invention.

FIG. 2 is to show a first blank sheet obtained by the first step of theprevious invention, wherein (A) is a plan view, (B) is a cross sectionalview taken along the line a—a in the (A), (C) is a cross sectional viewtaken along the line b—b in the (A), and (D) is a cross sectional viewtaken along the line c—c in the (A).

FIG. 3 is to show a second blank sheet obtained by the second step ofthe second step of the previous invention, wherein (A) is a plan view,(B) is a cross sectional view taken along the line a—a in the (A), (C)is a cross sectional view taken along the line b—b in the (A), and (D)is a cross sectional view taken along the line c—c in the (A).

FIG. 4 is to show a first blank sheet obtained by the second step of thesecond step of the previous invention, wherein (A) is a plan view, (B)is a cross sectional view taken along the line a—a in the (A), (C) is across sectional view taken along the line b—b in the (A), and (D) is across sectional view taken along the line c—c in the (A).

FIG. 5 is to show a second blank sheet obtained by the second step ofthe second step of the previous invention, wherein (A) is a plan view,(B) is a cross sectional view taken along the line a—a in the (A), (C)is a cross sectional view taken along the line b—b in the (A), and (D)is a cross sectional view taken along the line c—c in the (A).

FIG. 6 is to show a second blank sheet obtained by the second step ofthe second step of the previous invention, wherein (A) is a plan view,(B) is a cross sectional view taken along the line a—a in the (A), (C)is a cross sectional view taken along the line b—b in the (A), and (D)is a cross sectional view taken along the line c—c in the (A).

FIG. 7 is to show a second blank sheet obtained by the second step ofthe second step of the previous invention, wherein (A) is a plan view,(B) is a cross sectional view taken along the line a—a in the (A), (C)is a cross sectional view taken along the line b—b in the (A), and (D)is a cross sectional view taken along the line c—c in the (A).

FIG. 8 is an enlarged view of the cross sectional portion in FIG. 7(D).

FIG. 9 is a partially cross sectional, side view to show a first exampleof the embodiment of the present invention.

FIG. 10 is an enlarged cross sectional view taken along the line X—X inFIG. 9.

FIG. 11 is a partially cross sectional side view to show a secondexample in the embodiment of the present invention.

FIG. 12 is an enlarged cross sectional view taken along the line Y—Y inFIG. 11.

FIG. 13 is to show a first blank produced in the first step in the firstexample of the embodiment of the present invention, wherein (A) is aplan view and (B) is a side elevational view with reference to (A).

FIG. 14 is to show a second blank produced in the following step,wherein (A) is a plan view, and (B) is a side elevational view withreference to (A).

FIG. 15 is a plan view to show another example of a second blank underprocessing.

FIG. 16 is to show a third blank produced in the following step, wherein(A) is a plan view, and (B) is a side elevational view.

FIG. 17 is to show a fourth blank produced in the following step,wherein (A) is a plan view, and (B) is a side elevational view.

FIG. 18 is an end view to show a state during a process to produce afirst intermediate blank in the following step.

FIG. 19 is to show the first intermediate blank obtained, wherein (A) isan end view, and (B) is a side elevational view.

FIG. 20 is a plan view to show a bending position upon producing thefirst intermediate blank from the fourth blank.

FIG. 21 is an end view of the intermediate blank to show that thepre-state and post-state of the bending process and thickening processaffect the width of the thickened portion.

FIG. 22 is an end view to show a state during the process to obtain thesecond intermediate blank.

FIG. 23 is an end view of the second intermediate blank obtained.

FIG. 24 is a cross sectional view to show a state during the process toobtain the third intermediate blank.

FIG. 25 is to show the third intermediate blank obtained, wherein (A) isa cross sectional view, and (B) is a side elevational view.

DISCLOSURE OF THE INVENTION

The sheet-metal rocker arm 1 of this invention is formed by punching onesheet of metal member to form a blank having a specified shape andthrough holes, and by performing a bending process for this blank basedon a press process, such that a pair of nearly parallel side wallsections and a connection section that connects the edges in the widthdirection of both of these side wall sections are formed, and that atleast one pair of circular holes are formed at corresponding locationsin alignment in both side wall sections, and then by deforming in thethickness direction the middle of the connection section, so that anengagement section is formed on one surface of the connection sectionthat is more concave than the other surface of the connection section.Moreover, as this engagement section is formed, a protrusion protrudesin an embanked shape from the other surface of the connection section toform a bulge section having a trapezoidal cross-section. Theconstruction described above is the same as for the sheet-metal rockerarm of the previous invention as mentioned above.

Furthermore, in the case of the sheet-metal rocker arm of thisinvention, both edges in the width direction of the center section ofthis bulge section, which corresponds to the top of the aforementionedtrapezoid, are located inside in the width direction than both edges ofthe engagement section.

It is preferred to make the thickness of the engagement section greaterthan the thickness of both side wall sections by increasing thethickness of the connection section from which the engagement section isformed.

It is further preferred that, of the thicknesses of the connectionsection, the ratio t/T of the thickness t of the thinnest section, orthe distance between the inclined section on both sides in the widthdirection of the bulge section and the corner sections of the engagementsection, with respect to the thickness T of the thickest section, or thedistance between the center of the bulge section and the engagementsection, be 0.5 or greater.

Similar to the sheet-metal rocker arm of the previous invention asmentioned above, the sheet-metal rocker arm of this invention, asdescribed above, is formed in a single body from a single sheet of sheetmetal, so that there is no need for joining a plurality of members thathave been made separately, and it is possible to reduce the number ofprocesses, while at the same time it is possible to prevent increasingmanufacturing costs and worsening precision, and do away with the needfor complicated equipment for assembly and positioning, and it ispossible to produce a high quality sheet-metal rocker arm at a lowercost.

Particularly, in the case of the sheet-metal rocker arm of thisinvention, a bulge section provided on the side opposite to theengagement section in the thickness direction of the connection section,and both edges in the width direction of the center of the bulgesection, which corresponds to the top of the trapezoid in cross sectionof the bulge section, are further inside in the width direction thanboth sides in the width direction of the engagement section, so thatwhen forming the engagement section and bulge section, no shear force isapplied to any part of the connection section. Therefore, it is possibleto make it more difficult for damage due to cracking or the like tooccur in the connection section.

Moreover, when the thickness of the connection section provided with theengagement section is made to be greater than the thickness of both ofthe side wall sections, the work of increasing the thickness of thisconnection section can be performed by just a pressing process withoutthe need for special equipment, so that it is possible to keep down theinvestment in equipment, and by saving energy by automated processing,it is possible to manufacture a high-quality sheet-metal rocker arm atlow cost. In addition, regardless of whether or not the sheet-metalrocker arm is formed from one sheet of metal of uniform thickness, it ispossible to make the thickness of the connection section, which includesthe engagement section, greater than the thickness of the pair of sidewall sections. It is also possible to reduce the stress forces that acton the sheet-metal rocker arm and maintain the strength and rigidity ofthe sheet-metal rocker arm without unnecessary weight increase. Thethickness of both of the side wall sections can be such that it ispossible to maintain the strength and rigidity that are required forboth of the side wall sections, and does not need to be any greater thannecessary. Also, it is possible to reduce the width of the sheet-metalrocker arm, which is the distance between the outside surfaces of bothof the wall sections. This makes it easier to design the sheet-metalrocker arms, so that it can be assembled in the limited space inside theengine.

Furthermore, when the ratio t/T of the thickness t of the thinnest partof the connection section and the thickness T of the thickest part,which is the distance between the center of the bulge section and theengagement section, is 0.5 or greater, the force applied to theconnection section during use of the sheet-metal rocker arm becomesuniform, making it possible to even more effectively prevent damage tothe connection section.

Also, with the method for manufacturing a sheet-metal rocker arm of thisinvention, the sheet-metal rocker arm is manufactured such that a blankhaving a specified shape and through holes is formed by punching onesheet of metal, that a bending process is applied to the blank by apress ing process so as to form a pair of nearly parallel side wallsections and a connection section that connects the edges in the widthdirection of those side wall sections, that at least one pair of throughholes are formed at locations in alignment in both of the side wallsections, and that at least one engagement section is formed on part ofthe connection section. In addition, the thickness of the connectionsection where the engagement section is formed is greater than thethickness of both of the side wall sections.

With the manufacturing method of this invention for manufacturing asheet-metal rocker arm, the thickness of the engagement section isincreased by pressing the protruding section, which protrudes from theends that are next to the part of the blank that becomes the engagementsection, in both directions of the blank toward the part that becomesthe engagement section. After the thickness of this has been increased,there is a process for forming th is section into the engagementsection. Both directions mentioned here are the directions parallel tothe front and rear surfaces of the blank.

Preferably, one metal material such as sheet metal is fed from anuncoiler or the like and punched by performing a sequential punchingprocess in synchronization with the feeding of this metal material, sothat a continuous section is formed such that it is located in thecenter in the width direction of this metal material, and a pair ofblanks are formed such that they extend outward in opposite directionsfrom both edges in the width direction of this continuous section at theportion where the phase in the length direction of each side matcheseach other. A protruding section is provided on the opposite sides ofthese blanks in pair, respectively. Then by pressing both of theprotruding sections in a direction toward each other, the thickness ofpart of these blanks is increased. Also, in any of the processes afterthis process, these blanks are cut and removed from the continuoussection.

Also, preferably, after increasing the thickness of part of the blankthat will become the engagement section, it is annealed in an annealingprocess and then a through hole is formed in the center of this blank,then the blank is bent at two locations with the through holetherebetween in the same direction to form a pair of side wall sections.

Moreover, preferably, after the thickness of the part of the blank thatwill become the engagement section has been increased, the through holein the center of this blank is formed such that its width is nearly thesame as that of the increased-thickness part, and such that the phase inthe width direction of the blank corresponds with that of the sectionwith the increased-thickness part. Then, at two locations on the blankin between which the through hole is located, that is along the sectionwhere the thickness was increased and along the section that nearlycorresponds to both edges in the width direction of the through hole,the blank is bent in the same direction to form a pair of side wallsections. The places of the blank that are bent when forming the sidewall sections are located along the section where the thickness wasincreased and along the section that nearly corresponds to both edges inthe width direction of the through hole.

Furthermore, preferably, after the sheet-metal rocker arm is processedto its final form, heat treatment, such as carbonization heat treatment,is performed for hardening the surfaces of the sheet-metal rocker arm,and then processing is performed to remove to the intergranularoxidation layer from the surface of the sheet-metal rocker arm. It ispreferred that the process for removing this intergranular oxidationlayer be a method of striking the surface of the sheet-metal rocker armwith particle matter like media, such as in shot blast or barrelprocessing.

Particularly, in the case of the sheet-metal rocker arm of thisinvention, it is possible to make the thickness of the connectionsection where the engagement section is formed much thicker than thethickness of both side wall sections. Therefore, in spite of the factthat the sheet-metal rocker arm is formed from one blank with uniformthickness, it is possible to make the thickness of the connectionsection, including the engagement section, much thicker than thethickness of the pair of side wall sections. Accordingly, it is possibleto greatly reduce the stress that is applied to the connection section,including the engagement section, and to secure the strength andrigidity of the sheet-metal rocker arm without having to unnecessarilyincrease the weight. Also, the thickness of both of the side wallsections can be such that it is possible to secure the strength andrigidity that are required for both of the side wall sections, and doesnot need to be any greater than necessary. Accordingly, it is possibleto reduce the width of the sheet-metal rocker arm, which is the distancebetween the outside surfaces of both of the side wall sections. Thismakes it easier to design the sheet-metal rocker arms so that it can beassembled in limited space inside the engine.

Also, by providing a pair of blanks connected to each other by acontinuous section, and having a protruding section which protrude fromthe opposing sides of the blanks and by pressing the protruding sectionsin a direction toward each other, to partly increase the thickness ofeach blank, it is possible to cancel the force applied to both blanksduring this pressing process. Therefore, it is possible to reduce therigidity of the portion that receives the force applied during thispressing process, and thus it is possible to simplify and reduce thecost equipment used.

Also, when annealing of the blank is performed before bending part ofthe blank to form the pair of side wall sections, it is possible tosoften the portion that was hardened by work-hardening during thepressing process, and remove any residual stresses. Therefore, it notonly becomes easier to perform the work of forming the side wallsections, but it is also possible to effectively prevent damage due tocracking from occurring in the bent sections.

Also, by matching the portion of the blank having the increasedthickness, which will become the engagement section, with the throughhole in the width and phase in the width direction, and by making theposition of the bending when forming the side wall sections nearly matchwith the both ends in the width direction of the through hole, it is notonly possible to easily perform the work of forming the side wallsections, but it is also possible to effectively prevent damage due tocracking from occurring in the bent sections.

Furthermore, by performing a process for removing the intergranularoxidation layer from the surface of the sheet-metal rocker arm afterperforming heat treatment for hardening the surface of the sheet-metal,it is possible to remove minute grooves that cause damage such ascracking, and improve the durability of the sheet-metal rocker arm. Inthis case, by performing the process for removing this intergranularoxidation layer by a method of striking the surface of the sheet-metalrocker arm with particle matter like media, such as in shot blast orbarrel processing, it is possible to produce residual compression stressin the surface layer portion of the sheet-metal rocker arm and to moreeffectively prevent the occurrence of damage due to cracking.

Best Embodiments to Work the Invention

FIGS. 9 and 10 show a first example of the embodiment of the sheet-metalrocker arm of this invention. This invention is characterized by thecross-sectional shape of the aforementioned connection section 3 forsufficiently maintaining the durability of the connection section 3 andimp roving the strength of the engagement section 6, even when theelastic force of the return spring that energizes the valve unit whosebase end is in contact with the engagement section 6 that is formed onone surface bottom surface in FIGS. 9 and 10) of the connection section3 is large, and therefore when the force applied to the engagementsection 6 is large, the construction of the other parts of thesheet-metal rocker arm 1 are the same as in the aforementioned previousinvention, so the same numbers will be given to identical parts, and anyredundant explanation will be omitted or simplified. This explanationwill center on the characteristics of this invention.

First, the construction, function and effect of one feature of theinvention will be explained. As in the ase of the aforementionedprevious invention, the engagement section 6 is formed by deforming thecenter section in the width direction of the connection section 3 (frontand rear direction in FIG. 9, and left and right direction in FIG. 10)in the thickness direction (up and down direction in FIGS. 9 and 10). Asthis engagement section 6 is formed on the one surface (lower surface inFIGS. 9 and 10) of the connection section 3 such that it is more concavethan the other parts of the connection section 3, the other surface(upper surface in FIGS. 9 and 10) of the connection 3 protrudes in abanked shape to form a bulge section 8 with a trapezoidal cross section.The cross-sectional shape of this bulge section 8 in the width direction(front and rear direction in FIG. 9, and left and right direction inFIG. 10) of the sheet-metal rocker arm 1 is a trapezoid shape. Also, onboth sides of the center section 20 of the bulge section 8, whichcorresponds to the top of the trapezoid, a pair of inclined sections 21are formed such that they are inclined toward the engagement section 6in a direction away from the center section 20.

Particularly, in the case of the sheet-metal rocker arm of thisinvention, the width W₂₀ of the center section 20 is less than the widthW₆ of the engagement section 6 (W₂₀<W₆). Also, both ends in the widthdirection (left and right direction in FIG. 2) of the center section 20are located further inside in the width direction than both ends in thewidth direction of the engagement section 6. Therefore, in the exampleshown in the figures, the center position in the width direction of thecenter section 20 matches with the center position in the widthdirection of the engagement section 6 (in alignment in the phase in thewidth direction matches). The amount that the width W₂₀ of the centersection 20 is less than the width W₆ of the engagement section 6 isregulated within a range such that shear forces do not occur inside theconnection section 3 when pressing the engagement section 6.Accordingly, the width W₂₀ of the center section 20 is 80% or less thanthe width W₆ of the engagement section 6 (W₂₀≦0.8 W₆), and even morepreferable, 60% or less (W₂₀≦0.6 W₆).

The engagement section 6 and bulge section 8 are form ed by stronglypressing the part corresponding to the connection section 3 on the endof the second intermediate blank 18 (see FIG. 5) between the pressingdie and cradle die of a press apparatus. In th case of this ininvention, since the width W₂₀ of the center section 20 of the bulgesection 8 is less than the width W₆ of the engagement section 6 asdescribed above, when performing the pressing process above, there is noshear force applied to both ends in the width direction (dot and dashline γ in FIG. 10) of the engagement section 6, which is formed on partof the connection section 3 in the width direction. Rather, acompression force is applied to both end sections between opposite endedges of the pressing die for forming the engagement section 6 and thepart of the cradle die that faces the pressing die and which forms theinclined section 21 of the bulge section 8, and makes the structure ofboth end sections dense. As a result, no internal deformation that wouldcause damage such as crack ing occurs in the end sections, and so it isdifficult for damage such as cracking to occur in both of the endsections in the width direction of the engagement section 6 even whenlarge forces are repeatedly applied to the engagement section 6 over along period of time.

Next, the construction, function and effect of another feature of theinvention will be explained. The thickness of the aforementionedconnection section 3 is the thinnest thickness “t” between the inclinedsections 21 that are on both sides in the width direction of the bulgesection 8, and the corner sections 22 of the engagement section 6. Incontrast, the thickest thickness T is between the center section 20 ofthe bulge section 8 and the engagement section 6. In the case of thissheet-metal rocker arm, the ratio t/T of the thicknesses t and T is 0.5or greater.

By making the ratio t/T between the thickness t at the thinnest part ofthe connection section 3 and the thickness T at the thickest part 0.5 orgreater, the force applied to the connection section 3 becomes uniform,while the sheet-metal rocker arm 1 is in operation which makes itpossible to even more effectively prevent damage to the connectionsection 3. In other words, when the t/T is too small, stress isconcentrated at the areas between the inclined section 21 and the cornersections 22 of the engagement section 6 when the sheet-metal rocker armsis in operation, making it easy for damage such as cracking to occur inthose areas. Table 1 below shows the test conditions and the results fortests that were performed to find out the effect that the ratio t/T hason durability of these areas.

TABLE 1 1 2 3 4 5 6 7 8 9 10 Thickness T 3.50 3.75 3.60 3.65 3.45 3.553.60 4.60 4.50 4.40 Thickness t 2.55 1.70 2.20 2.70 2.55 2.65 2.70 2.652.84 2.65 Ratio t/T 0.73 0.45 0.61 0.74 0.74 0.75 0.75 0.58 0.63 0.60Result ◯ X ◯ ◯ ◯ ◯ ◯ ◯ ◯ ◯

In this test, 10 samples were prepared having different ratios t/T a ndan endurance test was performed under the same conditions similar to theactual operating conditions {a compression force of 1051.54 N (107.3kgf) was repeatedly applied to the engagement section 6 a}. In Table 1,the numerical values for the thicknesses t and T are in the unit of rm.Also, of the codes showing the test results, ‘◯’ indicates that nodamage due to cracking occurred, and ‘X’ indicates that damage didoccur. As can be clearly seen from the test results in Table 1, damageoccurred when the ratio t/T was less than 0.5, however became difficultto occur when the ratio t/T was 0.5 or greater. Accordingly, when thewidth W₂₀ of the center section 20 is less than the width W₆ of theengagement section 6, and the ratio t/T is 0.5 or greater, it ispossible to improve the durability of the sheet-metal rocker arm evenmore.

Next, FIGS. 11 and 12 show a second example of the embodiment of thesheet-metal rocker arm of this invention. In the case of the sheet-metalrocker arm 1 of this example, the depth of the groove-shaped cornersections 22 on both sides in the width direction of the engagementsection 6 is less than in the case of embodiment 1 described above, andthe width W₂₀ of the center section 20, which corresponds to the top ofthe trapezoidal cross section of the bulge section 8, is less than thedistance D₂₂ between both corner sections 22. The amount that the widthW₂₀ of the center section 20 is less than the distance D₂₂ between bothcorner sections 22, is also regulated within a range such that nointernal shear stress is applied to the connection section 3 during thepressing process of the engagement section 6. For example, the width W₂₀of the center section 20 is 80% or less than the distance D₂₂ betweenboth corner sections 22 of the engagement section 6 (W₂₀≦0.8 D₂₂), andeven more preferable, 60% or less (W₂₀≦0.6 D₂₂).

In the case of the embodiment constructed as described above, it ispossible to effectively prevent unwanted stress from occurring in theconnection section 3 when forming the engagement section 6. In otherwords, when forming the engagement section 6, part of the connectionsection 3 is pressed up a little as shown in FIGS. 11 and 12 whenforming both corner sections 22. In the case of this embodiment, theentire corner sections 22 are located in the part that corresponds tothe inclined sections 21 of the bulge section 8, so forces that occurwhen forming the corner sections 22 do not cause shear stress which isharmful from the aspect of securing durability.

Furthermore, in the case of the sheet-metal rocker arm 1 of thisembodiment, the constricted sections 12 a, 23 b that are formed in thearea next to the connection section 3 and second connection 4 in themiddle of one edge (lower edge in FIG. 11) of the left and right sidewall sections 2 are smaller than in the first embodiment describedabove, the position of the innermost end (the top of the arc) of theseconstricted sections 23 a, 23 b is shifted downward in FIG. 11. Also,the length between these constricted sections 23 a, 23 b and theperipheral edge of the circular holes 5 for supporting both ends of thepivot shaft for roller support is made longer. A large force is appliedto the inner peripheral surface of the circular hole 5 as the end of thepivot shaft is fitted inside the circular hole 5 and spread by crimping,and therefore tensile stress due to the large force is applied to theportion between these constricted sections 23 a, 23 b and the peripheraledge of the circular hole 5. However, as this distance is lengthened,the stress in this portion is lessened, thus making it more difficultfor damage due to cracking to occur in this portion. In the case of thesheet-metal rocker arm 1 of this invention, this construction makes itpossible to improve the durability even more when compared with thefirst embodiment described above.

FIGS. 13 to 25 show a first example of the manufacturing method for thesheet-metal rocker arm of this invention. A feature of this invention isin a method for sufficiently increasing the thickness t₃ of theconnection section 3 in order to sufficiently secure the durability ofthe connection section 3 and to improve the strength of the engagementsection 6, even when the force applied to the engagement section 6becomes large due to an increased elastic force of the valve spring,which energizes the valve unit the base end of which comes in contactwith the engagement section 6 that is formed on one surface of theconnection section 3 (see FIGS. 22 and 23). The construction of theother parts of the sheet-metal rocker arm that is manufactured by themanufacturing method of this invention is the same as for thesheet-metal rocker arm 1 of the previous invention shown in FIGS. 1 and7, so any redundant explanation will be omitted or simplified. Theexplanation below will center on the features of this invention.

In the case of manufacturing a sheet-metal rocker arm with themanufacturing method of this invention, first, in a first process, afirst blank 118 is made as shown in FIG. 13(A) and FIG. 13(B). That is,in this first process, a sufficiently rigid metal sheet (flat sheet orcoiled sheet), such as carbon steel sheet having a thickness of 3 to 4mm, is supplied between the punching die and cradle die of a pressapparatus not shown in the figure, and the first blank 118 is punchedout and formed between these dies. As shown in FIG. 13(A), this firstblank has a square or rectangular main section 119 and a square orrectangular protruding section 120 that is formed at the center of oneedge (top edge in FIG. 13(A)) of the main section 119. This protrudingsection 120 protrudes from the part of the first blank 118 that willbecome the engagement section 6, specifically from the edge adjacent tothe center of the top edge of the main section 119 shown in FIG. 13(A).

Next, in a second process, by performing the thickness-increasingprocess, called upsetting, which is a feature of this invention, on thefirst blank 118 described above, a second blank 121 is formed as shownin FIG. 14(A) and FIG. 14(B). This thickness-increasing process isperformed by pressing the protruding section 120 shown in FIG. 13(A) inthe surface direction of the first blank 118 (downward in FIG. 13(A) toFIG. 14(B)) toward the edge of the main section 119, which will becomethe engagement section 6. In other words, the main section 119 of thefirst blank 118 is set on a cradle die (not shown in the figure) thathas a shape corresponding to the shape of the second blank 11, and theprotruding section 120 is pressed by the pressing die (also not shown inthe figure) toward the main section 119. The main section 119 is tightlyfitted onto the cradle die such that only the thickness of the space ofthe section that corresponds to the engagement section 6 is increased bythe amount corresponding to that of the engagement section 6. Bystrongly pressing the protruding section 120 with the pressing dietoward the main section 119, with the main section 119 of the firstblank 118 set into the cradle die in this way, the thickness in thecenter of the edge of the main section 119, which will become theengagement section 6, is increased to obtain the second blank 121 asshown in FIGS. 14(A) and 14(B). This second blank 121 has a thicksection 122 formed in the area in the center of the edge of the mainsection 119, which will become the engagement section 6, where thethickness is greater than the thickness of the other parts.

In this second process, when strongly pressing the protruding section120 toward the main section 119, by providing a pair of first blanks118, as shown in FIG. 15, and by pressing the protruding sections 120that protrude from opposite sides of the pair of first blanks 118 in adirection toward each other, it is possible to reduce the rigidity ofthe portion that receives the force in this pressing work, or in otherwords, of the portion that supports the cradle die, and thus it ispossible to simplify and lower the cost of the equipment.

In other words, by feeding an elongated sheet of metal material from anuncoiler and by performing a sequential punching process insynchronization with the feeding of this metal material, a continuoussection 123 is formed such that it is located in the center in the widthdirection of this metal material, and a pair of opposing first blanks118 are formed such that they extend from both edges in the widthdirection (left and right direction in FIG. 15) of this continuoussection 123 specifically from the portion where the phase in the lengthdirection (up and down direction in FIG. 15) of each side matches eachother, outward in opposite directions. Then by pressing both of theprotruding sections 120 of the opposite sides of these first blanks 118in a direction toward each other, the thickness of part of these firstblanks 118 is increased to form the aforementioned second blanks 121.Also, in any of the processes that are performed after this process ofincreasing the thick ness, these second blanks 121 may be cut andremoved from the continuous section 123.

By forming these first blanks 118 into second blanks 121 as describedabove, it is possible to prevent the cradle dies from being moved evenwhen the support rigidity of the cradle dies, in which the main sections119 of these first blanks 118 are set, is decreased. In other words,with these cradle dies abutted to each other directly or by way ofanother connection member, the forces that are applied to the cradledies from the pressing dies by way of the first blanks 118 cancel eachother out. Therefore, it is possible to decrease the rigidity of thepart that supports these cradle dies as described above and simplify theequipment and lower the cost thereof. This technique is not limited tothe manufacture of a sheet-metal rocker arm, but can be applied tomanufacturing methods of manufacturing all kinds of parts in which thethickness of the part of the sheet metal is increased by an upsettingprocess. Also, the pair of blanks can be formed in any manner to besymmetrical on both sides of a joint such as a connection section, anddoes not necessarily have to be made by being punched out from a longpiece of sheet metal fed from an uncoiler.

In any ca se, in the third process that follows, a punching process(piercing) is performed on the second blank 121, shown in FIGS. 14(A)and 14(B), to form a third blank 124 as shown in FIGS. 16(A) and 16(B).That is, in the third process, an hourglass-shaped through hole 11 isformed in the center of the second blank 121 such that it has nearly thesame width as the thick section 122, and such that it matches the thicksection 122 in the phase with respect to the width direction of thesecond blank 121.

Chamfering is performed on the third blank 124, manufactured asdescribed above, to remove any burrs from the peripheral edge of thethrough hole 11, and then in a fourth process, trimming and cuttingprocess are performed to remove any excess material around theperipheral edge of the main section 119 whereby a fourth blank 125 isformed as shown in FIGS. 17(A) and 17(B). The shape of this fourth blank125 is nearly the same as the second blank 13 (see FIG. 3) of theaforementioned previous invention, except that the thickness of theconnection section 3 that will become the engagement section 6 hasalready been increased.

The construction of the press apparatus for performing the processesdescribed above is not especially set, however, from the aspect ofimproving processing efficiency, it is preferable that a sequential-feedpress is used for performing the processes from the first blank 118shown in FIGS. 13(A) and 13(B) to the fourth blank 125 shown in FIGS.17(A) and 17(B). In the case of a sequential-feed press that uses asingle die for multiple processes, it is possible to improve theprocessing efficiency because it is possible to reduce the amount thatthe object being processed must fed. On the other hand, in the bendingprocess described later and as shown in FIGS. 18 to 25, a transfer pressis preferred. In a transfer press, the dies used in each processes aredifferent, so it is difficult to improve the processing efficiency sincethe amount that the object being processed must be fed increases,however, since the it is easier to manufacture the dies used, it ispossible to reduce the costs by reducing equipment costs.

Chamfering is performed on the fourth blank 125 that is manufactured asdescribed above in order to remove the burrs around the outer peripheraledges, and then this fourth blank 125 is annealed in an annealingprocess. By annealing this fourth blank 125, it is possible to softenthe part that was hardened by work-hardening when performing thepressing work to form the thick section 122, and thus it is possible toremove any residual stress in the fourth blank 125 that occurred due tothat pressing work. Therefore, it not only becomes easier to perform thework of forming the side wall section 2 (see FIGS. 20 to 25) in thefollowing processes, but it is also possible to effectively preventdamage such as cracking from occurring in the bent sections. Whennecessary, in addition to the annealing process, multiple fourth blanks125 may be rubbed together and processed by barrel processing to removeany scales from the surface that occurred due to the annealing process,and to remove any burrs remaining on the edges.

After the fourth blank 125 has been annealed as described above, bothends in the width direction of this fourth blank 125 are bent in thesame direction as in the aforementioned previous invention, to form apair of side wall sections 2 that are parallel with each other. Thisbending process is performed, as shown in FIGS. 18 and 19, by a transferpress (not shown in the figures). When performing this bending process,the locations of the bending (corners on the inner peripheral side ofthe bend) are at two locations of the fourth blank 125 such that thethrough hole 11 is in between them, or as shown be the dot-dash lines α'in FIG. 20, at locations that nearly correspond with the through hole 11and both edges in the width direction of the thick section 122. In otherwords, both edges in the width direction of the fourth blank 125 arebent in the same direction with the dot-dash lines α'being the cornerson the inner peripheral side to form the aforementioned pair of sidewall sections 2 to provide a first intermediate blank 126 as shown inFIGS. 19(A) and 19(B).

When making this first intermediate blank 126, the location of bendingwhen forming the side wall sections 2 as described above is along thedot-dash line α' in FIG. 20, and nearly corresponds with the throughhole 11 and both ends in the width direction of the thick section 122,so not only is it possible to easily perform the work of forming theside wall sections 2, but it is also possible to effectively preventdamage such as cracking from occurring in the bent sections.

Moreover, as shown in FIG. 21(A), of the obtained first intermediateblank 126, the width W₃ of the connection section 3 that corresponds tothe thick section 122 is greater than the distance D₂ between the pairof side wall sections 2 of the first intermediate blank 126, and up tothe width W₁₇ of the first intermediate blank 17 (W₁₇≧W₃≧D₂). By makingthe width W₃ of the connection section 3 greater than the distance D₂between the pair of side wall sections 2, it is difficult for damagesuch as cracking to occur in the engagement section 6 of the connectionsection 3 even when large force is applied in the thickness direction ofthe engagement section 6. By performing the thickness-increasing processwith upsetting for the part corresponding to the connection section 3after bending the wall sections 2, the width of the thickness section122 becomes less than the distance D₂ between the pair of side wallsections 2, so it becomes difficult to secure sufficient durability whena large force is applied to the engagement section formed on the thicksection 122.

An engagement section 6 is formed on the connection section 3 of thisfirst intermediate blank 126, as shown in FIGS. 22 and 23, to form asecond intermediate blank 127, and a second engagement section 7 isformed on the second connection section 4, as shown in FIGS. 24 and 25,to form a third intermediate blank 128. It does not matter whether thework of forming the engagement section 6 is performed before or afterthe work of forming the second engagement section 7. Also, circularholes 5 (see FIG. 1 and FIG. 7) are formed at corresponding locations inalignment in the pair of the side wall sections 2, to form the finalshape of the sheet-metal rocker arm.

After forming the final shape of the sheet-metal rocker arm as describedabove, heat treatment such as carbonization is performed in order toharden the surface of the sheet-metal rocker arm. After heat treatment,processing to remove the intergranular oxidation layer on the surface ofthe sheet-metal rocker arm is performed. This process for removing theintergranular oxidation layer is performed by a method of striking thesurface of the sheet-metal rocker arm with particle matter like media,such as in shot blast or barrel processing.

By performing a process to remove the intergranular oxidation layer onthe surface of the sheet-metal rocker after performing heat treatment toharden the surface, it is possible to remove minute grooves that couldcause damage such as cracking, and thus making it possible to improvethe durability of the sheet-metal rocker arm. In other words, there areminute grooves on the surface of the intergranular oxidation layer, soif the intergranular oxidation layer is left as is, it becomes easy fordamage such as cracking to occur from the minute grooves during use.Therefore, the rocker arm is treated by the aforementioned process toremove the intergranular oxidation layer and minute grooves and make itmore difficult for damage to occur. By performing the process forremoving the intergranular oxidation layer using a method of strikingthe surface of the sheet-metal rocker arm with particle matter likemedia, such as in shot blast or barrel processing, residual compressionstress occurs in the surface layer of the sheet-metal rocker arm, and itis possible to even more effectively prevent the occurrence of damagesuch as cracking.

In the case of the sheet-metal rocker arm constructed as describedabove, the necessary finishing processes, such as polishing, have beenperformed for the surface of the engagement section 6 that comes incontact with the base end of the valve unit during use, and for thesurface of the second engagement section that comes in contact with thetip end of a rush adjuster during use, and then the pivot shaft androller are installed. With the method of increasing thickness, which isa feature of this invention, it is also possible to increase thethickness of other engagement section and not just for the valveengagement sections. Also, in the case of a mechanical-adjustment-typesheet-metal rocker arm, in which a screw hole is formed in the pivotengagement section and an adjustment screw is screwed into that hole, itis possible to secure the screw length between the screw hole andadjustment screw and increase the strength of that section.

Application to the Industry

This invention is constructed and functions as described above, andmakes it possible to manufacture a lightweight and low-cost sheet-metalrocker arm having sufficient durability, and thus makes it possible toreduce the cost and improve the performance of the engine in which therocker arm is installed.

1. A sheet-metal rocker arm formed by punching one sheet of sheet metalto form a blank having a specified shape and through holes, and byperforming a bending process for this blank based on a press process,and comprising a pair of nearly parallel side wall sections each havingan edge in the width direction and a connection section that connectsthe edges in the width direction of both of these side wall sections,and the side wall sections having at least one pair of circular holesformed at corresponding locations in alignment, and the connectionsection having an engagement section formed on one surface thereof bydeforming in the thickness direction the middle of the connectionsection, such that it is more concave than the other surface of theconnection section, and a bulge section provided on the other surfacethereof by being protruded in an embanked shape as this engagementsection is formed, the bulge section having a trapezoidal cross-section,wherein the center section of the bulge section, which corresponds tothe top surface of the trapezoid, has bo th edges in the width directionlocated further inside in the width direction than both edges in thewidth direction of the engagement section.
 2. The sheet-metal rocker armof claim 1, wherein the thickness of the engagement section is madegreater than the thickness of both side wall sections by increasing thethickness of the connection section in which the engagement section isformed.
 3. The sheet metal rocker arm of claim 2, wherein with thethicknesses of the connection section, the ratio t/T of the thickness tof the thinnest section, that is the distance between the inclinedsection on both sides in the width direction of the bulge section andthe corner sections of the engagement section, with respect to thethickness T of the thickest section that is the distance between thecenter of the bulge section and the engagement section, be 0.5 orgreater.
 4. A manufacturing method for manufacturing a sheet-metalrocker arm formed by punching one sheet of sheet metal to form a blankhaving a specified shape and through holes, and by performing a bendingprocess for this blank based on a press process, and comprising a pairof nearly parallel side wall sections each having an edge in the widthdirection and a connection section that connects the edges in the widthdirection of both of these side wall sections, and the side wallsections having at least one pair of through holes formed atcorresponding locations in alignment, and the connection section havingat least one engagement section formed on one part thereof, wherein thethickness of the engagement section in the connection section is largerthan the thickness of the both side wall sections, comprising a processwherein a protruding section is formed to protrude from the end next tothe part of the blank that becomes the engagement section, in thesurface direction of the blank toward the part that becomes theengagement section, and after the thickness of this part has beenincreased, for forming the engagement section in the part, in whichthere is a bulge section having a trapezoidal cross-section, wherein thecenter section of the bulge section, which corresponds to the topsurface of the trapezoid, has both edges in the width direction locatedfurther inside in the width direction than both edges in the widthdirection of the engagement section.
 5. The manufacturing method ofclaim 4, wherein a pair of blanks are formed by performing a punchingprocess on a metal material, and a continuous section is formed suchthat it is located in the center in the width direction of the metalmaterial, and such that the blanks extend outward in opposite directionsfrom both edges in the width direction of the continuous section, andthen by pressing both of the protruding sections on the opposite sidesof these blanks in pair in a direction toward each other, the thicknessof part of these blanks is increased, and then the blanks are cut andremoved from the continuous section.
 6. The manufacturing method ofclaim 4, wherein after increasing the thickness of part of the blankthat will become the engagement section, it is annealed in an annealingprocess after a through-hole is formed in the center of this blank, andbefore the blank is bent at two locations with the through-holetherebetween in the same direction to form a pair of side wall sections.7. The manufacturing method of claim 4, wherein after the thickness ofthe part of the blank that will become the engagement section has beenincreased, a through-hole is formed in the center of this blank suchthat width is nearly the same as that of the thickness-increasedsection, and such that the phase in the width direction of the blankcorresponds with that of the thickness increased section, and then, theblank is bent at two locations with the through-hole therebetween in thesame direction, at the section where the thickness is increased and atthe section that nearly corresponds to both edges in the width directionof the through-hole, to form a pair of side wall sections, wherein theplaces that are bent when forming the side wall sections are on thesection where the thickness was increased and the section that nearlycorresponds to both edges in the width direction of the through-hole. 8.The manufacturing method of claim 4, wherein after the sheet-metalrocker arm is processed to its final form, heat treatment is performedfor hardening the surfaces of the sheet-metal rocker arm, and thenprocessing is performed to remove to the intergranular oxidation layerfrom the surface of the sheet-metal rocker arm.